As of today, fluorescent lighting is commonly used as the illumination system of choice for office lighting.
To enable architects and interior designers to create interior styles that clearly distinguish one building from the other, however, there is an increasing need to integrate lighting in interiors as unobtrusively as possible.
Conventional luminaires based on fluorescent lighting are known to have a minimum thickness of approximately 50 mm. Illumination systems based on alternative light-sources which allow for thin luminaries on the other hand, such as for illumination systems including a number of light-emitting diodes (LEDs) and a light guide for mixing and distributing the light emitted by the LEDs, offer much more freedom in designing the luminaire.
Achieving a sufficient degree of mixing of light in the light guide is an important factor for obtaining improved viewing characteristics for a luminaire based on the light guide. Such improvements may include, for example, increased uniformity of the light out-coupled from the light guide, and reduced maximum brightness.
WO 2006/034831 discloses one approach for achieving such mixing, according to which the light guide is provided with pyramid-shaped out-coupling facets which form such an angle with the out-coupling face that nearly parallel light undergoes several reflections in the light guide before being out-coupled.
A drawback of the light guide described in WO 2006/034831 is that it requires in-coupled light to be highly collimated to function properly.